Paved roads are constructed from a variety of materials including concrete and asphalt. Asphalt roads provide several advantages among which is that it is rarely necessary to completely remove and reconstruct an asphalt road. Between major renovations it is common to repair smaller imperfections in the road surface, the most common of which are potholes. Typically potholes are filled with hot asphalt aggregate, which is then tamped and rolled to finish the repair.
Asphalt for use in repair is actually a mixture of materials. Typically asphalt comprises 5% asphalt/bitumen and 95% aggregates (e.g., stone, sand, gravel). Because asphalt/bitumen is highly viscous (due to the bitumen) it must be heated prior to mixing with the aggregate components, Typically, asphalt is produced on an industrial scale at asphalt plants. Once prepared, it is then dispensed to users who then transport the asphalt to the work site for use in effecting road repairs.
Typically mixing of asphalt/bitumen and aggregates is done at a temperature of about 150° C. Since the workability of the asphalt product depends on temperature, it is normally desirable to dispense and compact the asphalt before it cool to a temperature below a range from about 65-85° C. Thus, a significant problem in using asphalt for road repairs is in maintaining a proper working temperature of the asphalt from the time it leaves the plant until it is used to repair a road surface. A variety of prior art methods have attempted to address this problem.
In the past during road repair, hot asphalt material has been manually placed, and then compacted with standard rollers or tampers. More recently, a variety of mobile pothole patching vehicles have been designed to transport hot asphalt to a roadway in need of repair, and then to apply and tamp the asphalt at the repair site. In general, these vehicles comprise a cab for the operator, mounted on a vehicle chassis, the chassis also adapted to carry the asphalt storage hopper from which the asphalt is dispensed. For example, Canadian Patent Serial No. 2,026,463 disclose a mobile, self-propelled repair vehicle that makes use of a conveyor system to deliver asphalt from an on-board hopper to a pothole in a road, as well as means for compacting the asphalt in the pothole in order to effect a repair.
U.S. Pat. No. 5,988,935 (Dillingham) discloses an asphalt repair system having a dry radiant heat source located below the hopper to heat the asphalt mixture. One problem of this system is that the location of the heat source means that the asphalt mixture will be heated unevenly, and the heat source requires an additional source of fuel, increasing the cost of operation of the system. In addressing some of these issues U.S. Pat. No. 6,681,761 (Dillingham) further provides a damper system in order to retain heat within the heating chamber, with the damper being electronically controlled in response to temperature sensed within the body of the device.
U.S. Pat. No. 4,812,076 (Yant) describes an asphalt hopper heating system for heating the contents of a supply hopper mounted to a pavement-patching vehicle. The hopper tank is a double-walled construction such that there is a space between outer and inner sidewalls—exhaust gas is routed therethrough for heating the asphalt. There are a number of disadvantages with this prior art system—for example, this system requires the construction of a double-walled asphalt hopper, which increases the cost of production of the pavement-patching vehicle. In addition, heat transfers from the outside of the hopper, resulting in uneven heating of material in the middle of the asphalt load. Further, there is no means provided to ensure that the asphalt is maintained at a workable temperature.